“When we go swimming and we complain that our eyes are red, it’s because swimmers have peed in the water,” Michele Hlavsa, chief of the Center for Disease Control and Prevention’s healthy swimming program told TODAY. “The nitrogen in the urine combines with the chlorine and it forms what’s known as chloramine and it’s actually chloramine that causes the red eyes. It’s chlorine mixed with poop and sweat and a lot of other things we bring into the water with us.”

In fact, Hlavsa said, the stronger the chlorine smell at a pool, the more filled with pee it is. Healthy pools don’t smell like chemicals.

Shutterstock

Urine, not chlorine, causes eyes to burn and turn red while swimming.

It's not chlorine’s job to clean pee from a swimming pool. Its plate is full with E. coli and other germs. Once people start adding pee, poop, sweat, and dirt to the equation, it starts to try to tackle those instead, leaving it with little energy for anything else, said Hlavsa.

“I just don’t think this is on people’s radars,” she said. “People think waterborne disease is something that happens outside the United States. But really, we have plenty of them here.”

The recent CDC healthy swimming report found that one in five public wading or kiddie pools are closed because of violations, including improper PH levels, safety and disinfectant concentration. The CDC collected inspection data from five states in 2013 — the most recent year available — with the most public pools and hot tubs: Arizona, California, Florida, New York and Texas). Most inspections resulted in at least one violation.